The proposed merger of NYSE Euronext and Deutsche Börse presents both threats and opportunities for rival exchanges, said the chief executive of London Stock Exchange.

"On paper, the combination of two such very large companies represents a challenge to anyone," said Xavier Rolet, in a joint interview with Tom Kloet, chief executive of Toronto Stock Exchange operator TMX Group, just hours after the companies had announced their own planned merger.

"When a big company comes together, there are clearly some threats, but there are also opportunities" for rivals, said Rolet. Those include picking up employees who leave or clients who become "disaffected" if integration of the different pieces isn't handled smoothly, the two chief executives said.

The proposed LSE-TMX merger shouldn't produce such tumult, since there's relatively little overlap between the businesses of two sets of exchanges, the pair said. The combination is "focused on revenue synergies, not on cost synergies," said Rolet.

Rolet also said the NYSE-Deutsche Börse news "vindicates our approach as partners coming together to improve our competitive position in a world that's getting smaller" as exchanges consolidate.

The LSE-TMX merger would create a group with combined revenue of around $1.6bn (€1.2bn), overseeing 6,700 listed companies. After the merger, LSE shareholders will hold around 55% of the combined company and TMX shareholders 45%. The group's exchanges will continue to operate under their respective local regulators.